The Punta Union pass is only reachable by foot or mule along the spectacular 50km Santa Cruz trail, part of which is an ancient Inca road.

BBC: Trekking Peru��s Santa Cruz trail

Fortunately, the lack of a direct road from Cuzco to Machu Picchu has stood in the way of cars and trucks intruding on the Inca ruins.

BBC: Eco-scorecard to the world��s great attractions